DLI: A dynamic listen interval scheme for infrastructure-based IEEE 802.11 WLANs

Abstract

To allow mobile devices to conserve energy, IEEE 802.11 standard specifies a power save mode (PSM). A station in PSM, i.e. a PSM-STA, will wake up at a predefined listen interval (LI) to receive frames buffered at the access point (AP) while it is sleeping. When a PSM-STA wakes up to receive a beacon and finds that there are no buffered frames, the PSM-STA experiences an unnecessary wakeup. In case of an unnecessary wakeup, the associated mode transition energy (i.e. from doze to awake and from awake back to doze) is wasted. According to the IEEE 802.11 standard, each STA chooses its own LI at the time of association, and the value chosen remains unchanged throughout its association duration. If LI=1, a STA wakes up at every beacon interval (BI). As a result, the data frame delay is minimized but the chance of unnecessary wakeup can be high. On the other hand, if a larger LI is used, the chance of unnecessary wakeup is reduced but the delay performance will suffer. Aiming at minimizing unnecessary wakeup without sacrificing delay performance, a dynamic listen interval (DLI) scheme is proposed in this paper. In essence, a STA increases its LI by one for every unnecessary wakeup experienced, and reset its LI to one when a necessary wakeup occurs. While more sophisticated schemes can be designed, we prefer this simple scheme for its compatibility with the existing standard. Simulation results show that when traffic is bursty, total energy consumption can be reduced without noticeable degradation in delay performance.